This invention relates to a method for preparing catalysts useful in the manufacture of maleic anhydride by the oxidation of hydrocarbons. More particularly, it is directed to the preparation of catalysts suitable for producing maleic anhydride from saturated hydrocarbons.
Maleic anhydride is of significant commercial interest throughout the world. It is used alone or in combination with other acids in the manufacture of alkyd and polyester resins. It is also a versatile intermediate for chemical synthesis. Significant quantities of maleic anydride are produced each year to satisfy these needs.
The prior art teaches that vanadium catalysts are well suited to the production of maleic anhydride from hydrocabons, and further, that vanadium catalysts wherein the valence of the vanadium is between about 3.8 and 4.8 are particularly well suited for the production of maleic anydride from saturated hydrocarbons. The prior art further teaches that phosphorus-vanadium-oxygen catalysts are particularly useful for the conversion of aliphatic hydrocarbons to maleic anhydride and discloses a number of ways of preparing such catalysts.
Many prior art procedures for the preparation of phosphorus-vanadium-oxygen catalysts teach that it is preferable to reduce the vanadium in solution to the tetravalent state. For example, these catalysts can be prepared by contacting phosphorus compounds and vanadium compounds under conditions to form the tetravalent vanadium and to form the catalyst precursor, and thereafter, calcining the resultant phosphorus-vanadium-oxygen compound.
Although the prior art procedures provide acceptable catalysts, it has now been found that a superior performing catalyst can be prepared by the process of the present invention.